Tank suspension

I've been curious ever since i started playing WoT about the Suspension.
When looking at the US shermans, German Tigers and the USSR their T34/85 and the top tier tanks mostly have the suspension like the M103.
They all have different suspensions.
Now im wondering. Wat suspenion is good and wat is bad? and why are there many different suspensions?

Suspensions are the same. It wasn't easy to find something that would fit all the required purposes.

I'm no suspension expert, but I'll try to explain the big lines:

Big wheels suspensions? Great for speed, easy to maintain, but if the wheels do not have the proper vertical freedom to follow a rough terrain, you might encounter some issues to maintain your speed.
Torsion bars suspension and leaf spring suspension were very sturdy and easy to maintain, but were also a bit rough and lacked the better offroad capabilities of springs.

Very often, it also depended of the industrial capacity of your country. Do you need something simple and easy to maintain in the field? Or something more complicated, but providing better offroad capacity.
Also, depending on the recoil or the weight repartition of the tank, you didn't necessary had a choice if you wanted the suspension to hold that weight.

Many suspensions hold pro and cons depending on your needs.

Some suspensions were unfit for swamps and cold climates and had a tendency to freeze or clog with mud and tree roots like the Panther:

Spoiler

The suspension consisted of front drive sprockets, rear idlers and eight double-interleaved rubber-rimmed steel road wheels on each side, suspended on a dual torsion bar suspension. The dual torsion bar system, designed by Professor Ernst Lehr, allowed for a wide travel stroke and rapid oscillations with high reliability, thus allowing for relatively high speed travel by this heavy tank over undulating terrain. However, the extra space required for the bars running across the length of the bottom of the hull, below the turret basket, increased the overall height of the tank and also prevented an escape hatch in the hull bottom. When damaged by mines, the torsion bars often required a welding torch for removal.[28]
The Panther's suspension was complicated to manufacture and the interleaved system made replacing inner road wheels time consuming. The interleaved wheels also had a tendency to become clogged with mud, rocks and ice, and could freeze solid overnight in the harsh winter weather of the Eastern Front. Shell damage could also cause the road wheels to jam together and become extremely difficult to separate.[29] Interleaved wheels had long been standard on all German half-tracks. The extra wheels did provide better flotation and stability, and also provided more armor protection for the thin hull sides than smaller wheels or non-interleaved wheel systems, but the complexity meant that no other country ever adopted this design for their tanks.[30] In September 1944, and again in March/April 1945, M.A.N. built a limited number of Panther tanks with overlapping, non-interleaved steel roadwheels originally designed for the Tiger II and late series Tiger I tanks. Steel roadwheels were introduced from chassis number 121052 due to raw material constraints.[31]
Source: Wikipedia

In a nutshell: Great offroad capacity, great speed, great weight repartition, but it was easily damaged or clogged, and required hours of work to maintain or repair as you needed to remove the first set of wheels to access the inside, interleaved ones.

Last, but not least, some suspensions also required specific material, not always available in time of war. As example, the German had troubles to obtain rubber for the Panzer wheels, and had to adapt suspensions accordingly.
Another example is the British Tortoise. The tank had a very complicated suspension but of great efficiency. It allowed it to only have a ground pressure of 0,84kg/cm², which is roughly the equivalent of an IS-2 for almost twice the size.
However this great suspension has a cost. There is no less than 200 grease points. I don't even want to imagine the oil/grease consumption of this monster. This tank would have left behind him a trail of devastation and greasy slime mixed with dirt. (And oh my, you do not want to be the guy cleaning that suspension as the end of the day.)

IMO Torsion bar suspension was the great leap forward, designed by an American guy called J Walter Christie in the 1920's, his tanks were bourght by serveral countries, 2 main ones where the British and the Russians, adopting this suspension gave a faster and more stable ride, Most not if all modern day tanks use this suspension system, inter leaved road wheels allowed the tank even greater stability due to the distance between the wheels riding on the tracks was less than spaced out wheels T34 spaced Panther closer I hope this helps and makes any sense

Also using torsion bar suspension gave a lager fighting compartment, because the bars were under the floor which took up very little space, spring suspension ie Sherman had a narrower fighting compartment( the overall width of a tank is governed by the width of transprotation ie Flat cars for the railway systems)

Uh, Christie's system had Jack all to do with torsion bars - which notably in Soviet designs *replaced* it. And AFAIK the 'bar concept was originally used in civilian cars...
Most armies seem to have settled on the torsion-bar solution already towards the end of WW2, presumably as a satisficatory compromise of diverse needs. The Brits however stuck to the wholly "external" Horstmann system as late as the Chieftain for whatever reason, and some newer MBTs use the fancy-pants but rather clever hydropneumatic system again originating in the civilian car industry.

What would interest me is how the proposed "Belville-washer" type suspension on the E-Series would have worked. On paper and what you can find on belville-washers that seemed to have been a great idea, however it was never adopted on any tank, indeed the only vehicle that used it as suspension was an airplane afaik. (Ju88 I believe....).

So any experts here giving a short pro and con list for this type of suspension?.....

I would say the biggest pro of the "Belville-washer" suspension shine in regard to the German economic situation, and the purpose of the E-serie.

The Entwicklung Serie main purpose was to standardize the tank production in 6 weight classes, to produce cheap, easy to make, and reliable tanks. Torsion bars had been decided too difficult and costly to make, and the big factories were getting bombed. Therefore, they needed something that could be ordered from small factories and contractors. As the washers could be churned out on most stamping machines, the German naturally turned toward that choice.
The complete bogie would be called "Einheitslaufwerk" ("Standard wheels" from my limited German knowledge).
It brought multiple advantage over the Torsion Bars :
- A floor escape hatch could be installed (as usually torsion bars runs under the tank, blocking all escape from that side)
- It was easy to maintain and replace, even on the field (You would usually need a torch to cut and remove a damaged torsion bar from a mine explosion)

You're forgetting the bogie system. I have no knowledge on US or german bogie suspension IRL, but I have experience on Soviet desing bogie system (T-26). On soft terrain it's OK, but on hard surface (stone, pavement, concrete) it is really really unconfortable. When I was driving T-26 (voluntery work in Finnish Armour museum), I allmost could feel every single stone in my back. Imagine driving it for 4 hours a day...

But... In that time (early 30's) there were not so many different suspensions around. Well, there were many but very few of them were even fairly usable on tanks.

On paper and what you can find on belville-washers that seemed to have been a great idea, however it was never adopted on any tank, indeed the only vehicle that used it as suspension was an airplane afaik. (Ju88 I believe....).

Here's a basic, but incomplete, primer:
Return Rollers:
In general those tanks that have return rollers have smaller diameter roadwheels, there are advantages and disadvantages to each:
Return Rollers / Top Run on Roadwheels
Puts top run of track as sprung weight/ Reduced logistics (fewer parts)
Flexibility of choice as to sprocket and idler diameter/ Reduced rolling resistance
Reduced weight of unsprung items/ Smoother inner surface
Reduced bending stresses on roadwheel rims/ Suspension protected behind wheels
Reduced bulk of logistics (smaller parts)/ Additional side protection
More roadwheels reduce wheel loading, increasing bearing life/ Lower speed and increased life of wheel bearings
More roadwheels give better spread of weight, reducing peak ground pressure/ Better self-cleaning of track and running gear
Loss of one or two wheels less serious/

Suspension Types:

Slow-motion
So-called because they were really only effective at slow speeds. The vertical block is fixed to the hull, and the beam pivoted from it. Leaf springs may be used, as well as coil springs, and the simplest form is shown - a more complicated version would have the two smaller wheels on their own beam, pivoted off the beam for the larger wheel, and this sub-beam would be separately sprung. Used on A9 and A10 cruisers, Valentine, Vickers 6-tonners and foreign variants (Russian T-26, Czech LT-35 etc.) among others.

Horstman
Horstmann (the man's name had a double "n" - his father was German, but the company name is Horstman) patented his suspension bogie in 1922. Adopted by the British and the Americans, Vickers light tanks and Bren/ Universal carriers etc., the suspension principle is still used today on, among others, Khalid, Centurion and Chieftain. Horstman bogies are favoured by the British due to the fact that they take up no room inside the vehicle (except for attachment points, and are easily replaced. Although this particular type is called Horstman, the original patent mentions the use of torsion bars (further down the page for this suspension) and the company currently make many other types, including hydrogas, hydrostrut and in-arm suspensions. 250 mm is a typical deflection figure for Horstman suspensions.

Coil spring
Merkava.

Christie
Designed by Walter J. Christie, who also designed fast tanks, the Christie suspension gave a very smooth ride, even at high speeds. Deflections on early Christie tanks were 350 mm or so, on the Cromwell they achieved a total (upwards bump and downwards rebound) of 416 mm. Used on the BT series, T-34, British cruisers from A13 up to and including Comet. The drawback is that the suspension requires internal hull space at the sides.

Belleville Washers
An extremely simple method of springing - the Belleville is a conical spring washer that increases in diameter and reduces in height when under load. Individually, each washer reduces by only a little, but when stacked on a shaft in numbers (top-to-top and bottom-to-bottom) then the percentage decrease in overall height can add up to a significant length. - a typical deflection for Belleville-type suspension is around 270 mm. Used on unbuilt German E-100 and the Swiss Pz. 61 and Pz. 68.

Torsion Bar
Shown from right-rear looking forwards, the arms are trailing. The torsion bar is fixed across the hull width and pinned at the end opposite the wheel, the end near the wheel is restrained from any movement but rotation. When the wheel is deflected it transmits this movement through the lever arm into the torsion bar which can only twist about its own axis (red arrows show how the amount of twist decreases along the length since one end is pinned). Maximum wheel deflection is limited by torsion bar length (which is limited by lower hull width) and strength of the steel used in the bar. Solutions found to the limited vertical travel of the roadwheel were a double-length torsion bar bent back upon itself or installing the bar inside a carefully-toleranced torsion tube. Torsion bars generally have a lower deflection limit than externally sprung systems, are vulnerable to mine damage, and difficult to replace. They also occupy internal space in the vehicle and require extra internal height.
The above sketch shows that, since each wheel is independently-sprung, each needs its own torsion bar. In most cases the bars are much closer together, so much so that the pinning block of one bar is incorporated into the rotating bearing housing for the other bar. This also shows why some tanks do not have their roadwheels directly in line with each when viewed from the side, (in fact as a young model-maker I was often convinced I'd missed a stage in the instructions when assembling a kit - the wheels didn't line up so I must have done something wrong!). Examples are Pzkpfw II Ausf. D, KV series, Panther, M48 onwards, AMX-30, Leopard 1 and 2.

Ignore the references to "sketches" since this is copied (without drawings) from my hyper book on tank technology. If you're really (seriously) interested try getting hold of Ogorkiewicz's Technology of Tanks (2 volumes - about £600 second hand )

Did they now? Hadn't know that, I just assumed they also use torsion bars but the afaik those tanks where pretty much regarded as failures, altough I believe it had to do more with the fire control system than the suspension but I am far from sure.

Now I know that belleville washers were economical a better choice for germany late in the war (as well as all the other obvious advantages which come from side mounted bogies instead of torsion bars) but what would interest me is how they would have performed compared to torsion bars or christie suspension for example.

Also, altough that might have been not an important factor during the war, with average lifespans of the tanks rather short, how maintainance intensive and durable are they compared to the other, more common suspensions?

The "best" kind of suspension is arguably torsion beams. Sturdy, simple and with good dampening performance. Back during WW2, they could get away with some very crude systems like for example the VVSS(Vertical Volute Spring Suspension) on the Shermans, because it was important to keep churning those tanks out as fast as possible. Nowadays, tanks are such a big, long-time investment that ease of manufacture isn't nearly as important as actual performance. Hence why pretty much all modern tracked AFV's that I can think of use torsion bars.

"Arguably" is the word here.
Torsion bars (not beams) are vulnerable to being damaged, if mounted externally, (and take a LONG time to repair) or take up valuable internal space (torsion bars inside the hull). Horstman type was preferred by we Brits since the entire unit could be removed by loosening a few bolts and replaced quite quickly.

"Arguably" is the word here.
Torsion bars (not beams) are vulnerable to being damaged, if mounted externally, (and take a LONG time to repair) or take up valuable internal space (torsion bars inside the hull). Horstman type was preferred by we Brits since the entire unit could be removed by loosening a few bolts and replaced quite quickly.

Sure didn't take up lot of internal space in the AFV's I've been in. Little over a hands width, depending on the size of the vehicle. You'll actually want a second floor anyway due to vastly increased protection that gives against mines and IED's. Easy to repair and replace too I'd say. With the Leopard I drove, it was just a case of removing the running wheel, unbolting a few bolts and pulling the whole thing out. Might be more troublesome of it's somehow been snapped in half though, with one end being left in the groves on the other side of the hull, but the internal floor can be removed relatively easy anyway.

IMO Torsion bar suspension was the great leap forward, designed by an American guy called J Walter Christie in the 1920's, his tanks were bourght by serveral countries, 2 main ones where the British and the Russians, adopting this suspension gave a faster and more stable ride, Most not if all modern day tanks use this suspension system, inter leaved road wheels allowed the tank even greater stability due to the distance between the wheels riding on the tracks was less than spaced out wheels T34 spaced Panther closer I hope this helps and makes any sense

Also using torsion bar suspension gave a lager fighting compartment, because the bars were under the floor which took up very little space, spring suspension ie Sherman had a narrower fighting compartment( the overall width of a tank is governed by the width of transprotation ie Flat cars for the railway systems)

Actually Christee did not invent torsion bar suspension, he invented swinging arm suspension which is similar in action but uses a coiled spring attached to the pivoting arm on which the wheel is attached.

I'm not entirely sure Christie patented sloped armour, since the principle was well-known from warship design (for example the Civil War ironclads had it). And was, in fact, incorporated (to an extent) in the WWI French Schneider CA1.

Christee was the first to employ it as a main feature, as opposed to an incidental feature, of a tank's design.

I forgot to add that he designed the first tank with a suspension system, the Christee M-1919 which was the competitor, after WW1, to Ford's light tank design.

The M-1919 had sloping frontal armour and looked like an early T-3 / BT-1 without the famous Christee suspension.

It was considered too advanced and too complicated for production, so the US Army went for the Ford design and then opted for a licence to build the French M-1917 instead. In 1939 the US built M-1917 made up 80% of the US Army's tank pool.

In its day, the M-1919 carried the thickest frontal armour ever mounted on a tank (12mm. @ 60 Degrees to give 25mm.) and had a top speed of 7 MPH.

Armament was the ubiquitous French 37mm. L.21. BB cannon and the world's first co-axial machine gun.

The "best" kind of suspension is arguably torsion beams. Sturdy, simple and with good dampening performance. Back during WW2, they could get away with some very crude systems like for example the VVSS(Vertical Volute Spring Suspension) on the Shermans, because it was important to keep churning those tanks out as fast as possible. Nowadays, tanks are such a big, long-time investment that ease of manufacture isn't nearly as important as actual performance. Hence why pretty much all modern tracked AFV's that I can think of use torsion bars.

Ol_Harmon, on 17 October 2012 - 09:08 PM, said:

"Arguably" is the word here.
Torsion bars (not beams) are vulnerable to being damaged, if mounted externally, (and take a LONG time to repair) or take up valuable internal space (torsion bars inside the hull). Horstman type was preferred by we Brits since the entire unit could be removed by loosening a few bolts and replaced quite quickly.

Exemple of torsion bars in a Leopard 1:

It doesn't take that much space, barely a dozen centimeters of height. The main Issue I would get with torsion bars is the inability to get a floor escape hatch. If the tank flip over, you will have a hard time to survive.
Some country also turned away fom torsion bars because of the specific alloy used in their creation. They are much more expensive and technically difficult to create than other suspensions.